I guess it's more of a meet the baby since they want to do it after the baby is born. Am I required to invite people? It would be very weird in my social circle/family to do this, but I don't want to offend my ILs for being so generous.
ETA: I should have been more clear -- this is for my second baby, not a second shower for my first. My first was born 4 years ago, and they threw me a shower then too in which all of my family and friends came.
Re: ILs want to host "second shower"
I think a "meet and greet" is a nice thing to do. I don't think people will feel obligated to bring a gift - but will bring one because they want to.
Not sure of what your family/circle of friends would feel like - but I wouldn't feel weird at all being invited to a meet and greet of a second child.